PTFE has been used as a key material of gland packing in a form of braided string. Gland packing is a sealant to prevent leakages of gas, liquid, and steam, thereby it is an essential part in all sorts of valves and pumps in power plants, factories, and petrochemical facilities. Gland packing is generally jammed into a stuffing box to seal a rotating or reciprocating shaft for the prevention of gas, liquid, and steam leakages. Gland packing requires a perfect sealability, thus PTFE braided packing should have high tensile strength as well as excellent durability.
Japanese Patent Publication No. 2004-244787 discloses a method of making PTFE filaments. In the method, after a heat treatment process of a biaxially drawn PTFE film, the PTFE filaments are obtained by slitting the film partially in length. The PTFE filaments correspond to the HDME PTFE yarn of the present invention. In the specification, the term ‘mixed PTFE powder’ means a PTFE powder including PTFE as a principal ingredient as well as other components.
A GORE® or GFO® fiber, prepared by mixing a PTFE powder with graphite, is used as a material of gland packing. Braided packing made by a GORE® or GFO® fiber is widely used in valves, rotational machineries, pumps, or agitators because it has chemical and thermal resistance due to the characteristics of PTFE and graphite.
However, the GORE® or GFO® fiber used in gland packing and the PTFE filaments of Japanese Patent Publication No. 2004-244787 have the limitation of tensile strength for the durability of gland packing.
The inventors develop a mixed PTFE powder and an HDME PTFE yarn with excellent tensile strength using the PTFE powder for gland packing. The HDME PTFE yarn of the present invention may also be applied to a timing belt in an internal combustion engine, a v-belt, automobiles, airplanes, high-speed trains, and rockets.